1. Field of the Invention
This invention relates to disperse dyed polyethylene fibers and dye blends used for their manufacture. More specifically, the invention relates to disperse dyed articles and especially disperse materials produced from flash spun plexifilaments. Processes for producing the disperse dyed polyethylenes and dye blends are also disclosed.
2. Description of the Prior Art
The inability to dye polyolefin fibers is well known and has been a long standing problem within the industry. Polyolefins are hydrophobic and they lack dye sites to which dye molecules may become attached. One approach to color polyolefin fibers has been to add colored inorganic salts or stable organometallic pigments to polymer melts prior to spinning. Nonvolatile acids or bases or materials such as polyethylene oxides or metal salts have also been added to polymers prior to fiber formation to increase the affinity of the fiber for disperse, cationic, acid or mordant dyes. Still another approach has been to chemically graft polyolefin fibers with appropriate monomers after fiber formation to improve dyeability. See Textile Fibers, Dyes, Finishes, and Processes: A Concise Guide, by Howard L. Needles, Noyes Publications, 1986, page 191.
Efforts to impart dyeability to polyolefins, and particularly polypropylene, by incorporating nitrogen-based polymer additives has also been disclosed. In U.S. Pat. No. 3,361,843 various incompatible, basic nitrogen-based polymers are added to polypropylene, given a treatment with high concentrations of certain acidic chemical reagents and then dyed in an acid dye bath. According to U.S. Pat. No. 3,653,803 dyeing of the polypropylene fiber is somewhat improved by the method of U.S. Pat. No. 3,361,843, but processing of the fiber is difficult due to the incompatible polymer, the dye fastness properties are not reliably reproducible and tinctorial strengths are not commercially sufficient. In U.S. Pat. Nos. 3,395,198 and 3,653,803, various compatible nitrogen-containing copolymers of ethylene and an aminoalkyl acrylate compound are disclosed which, when blended with polyolefins, render fibers formed from the blend acid dyeable. In U.S. Pat. No. 5,017,658 a fiber finishing agent is used in melt spinning dyeable polypropylene fibers obtained by blending a copolymer of an ethylene aminoalkyl acrylate with polypropylene.
Since polypropylene (PP) has properties rendering it highly useful for the manufacture of carpeting, still other efforts have been devoted to developing dyeable PP based fibers by modifying by the addition of functionalized copolymers capable of introducing polar sites with which dyes can associate. Such xe2x80x9cmodifiedxe2x80x9d polyolefins are disclosed in U.S. Pat. Nos. 5,468,259 and 5,550,192 wherein PP is combined with an ethylene-alkyl acrylate copolymer to provide 0.2 to 2.0 percent by weight alkyl acrylate in the fiber thus rendering the composition disperse dyeable under atmospheric pressure and conventional dyeing temperature conditions. A related procedure disclosed in U.S. Pat. No. 5,576,366 incorporates 0.1 to 15 percent by weight polyester with the ethylene-alkyl acrylate copolymer or other polar group-containing material. A method of disperse dyeing PP fibers of the above types which contain functional groups as a result of incorporating other polymers with the PP utilizing disperse dye mixtures is also disclosed in U.S. Pat. No. 6,039,767.
In a process disclosed in U.S. Pat. No. 6,054,215, disperse dyeable PP fibers are produced by making PP resin composition chips by dispersing 100 parts by weight of PP, 1-10 parts by weight of semi-crystalline functional high polymer, 0.05-5 parts by weight of amorphous functional polymer, and 0.1-3 parts by weight additives and melting and spinning the PP resin composition chips.
Procedures to effectively dye unmodified polyolefins, i.e., polyolefins having no added polar functionality, are needed. It would be particularly advantageous if disperse dyed polyethylene fibers and materials were available.
The present invention relates to disperse dyed polyolefins, particularly polyethylene (PE), to disperse dye mixtures and to a method of disperse dyeing. A significant feature of the invention is that polyethylene materials may be reliably disperse dyed to various shades and that the dyed materials exhibit good crocking characteristics. The polyethylene may be dyed as the fiber, yarn or fabric. Another significant advantage of the invention is that the dyeing is accomplished using conventional dyeing procedures and that the dye blends are obtained using combinations of commercially available disperse dyes. A further significant feature is that the disperse dye mixtures used are formulated utilizing known dye selection procedures.
More specifically, the invention relates to a process for disperse dyeing polyethylene based material comprising preparing a primary color dye blend comprising a plurality of disperse dyes from said primary color group, each of the selected plurality of disperse dyes present within the dye blend at a concentration of at least 75 percent but less than 100 percent of its determined maximum concentration which will produce crocking, and contacting the undyed polyethylene material with the disperse dye blend to dye the material.
The polyethylene is preferably a polyethylene homopolymer or copolymer of ethylene and a C3-8 xcex1-olefin having a melt index from 0.05 g/10 min to 50 g/10 min and density from 0.910 g/cm3 to 0.965 g/cm3. The process is particularly useful for disperse dyeing HDPE and LLDPE fibers and woven and nonwoven materials produced therefrom. The fibers may be obtained by either melt spinning or flash spinning processes; however, nonwoven materials from plexifilimentary polyethylene fibers produced in flash spinning operations particularly benefit when dyed with the disperse dye blends of the invention. Useful blue, red and yellow disperse dye blends are detailed hereafter.